feat: add scheduled metadata refresh for libraries

Add metadata_refresh_mode (manual/hourly/daily/weekly) to libraries,
with automatic scheduling via the indexer. Includes API support,
backoffice UI controls, i18n translations, and DB migration.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/indexer/src/worker.rs

@@ -27,6 +27,9 @@ pub async fn run_worker(state: AppState, interval_seconds: u64) {
             if let Err(err) = scheduler::check_and_schedule_auto_scans(&scheduler_state.pool).await {
                 error!("[SCHEDULER] Error: {}", err);
             }
+            if let Err(err) = scheduler::check_and_schedule_metadata_refreshes(&scheduler_state.pool).await {
+                error!("[SCHEDULER] Metadata refresh error: {}", err);
+            }
             tokio::time::sleep(scheduler_wait).await;
         }
     });